The operation of various types of mechanisms, machines, apparatuses, devices, and the like entails the rotation of a component (e.g., a rotor) about an axis of rotation such as the axis of a shaft driven by a motor. The rotation of any rotor and shaft about an axis is attended by some amount of imbalance in the forces and inertia resulting from the rotation, due to the imperfect distribution of mass of the rotor and shaft about the axis (including as a result of inhomogeneity in the material), tolerances or imperfections in the fabrication of the rotor or shaft and/or in coupling between the rotor and the shaft, and the imperfect stiffness of the shaft. Imbalance in the rotating system occurs when the center of mass (CM) and the principal axis of inertia of the system do not coincide with the axis of rotation. Imbalance may be quantified as mass time radius, i.e., the radial distance of the center of mass from the axis of rotation. Imbalance can cause unwanted vibrations, noise, stresses on the shaft and rotating elements, and wear on the bearings.
A balancing technique may be performed to correct for (reduce) the imbalance in a rotating system. The purpose of balancing is to shift the center of mass of the rotating system as close as possible to the axis of rotation, and to bring the principal axis of inertia as close as possible into coincidence (in line) with the axis of rotation. The center of mass can be shifted by performing a single-plane (or static) balancing of the rotor. Such a solution, however, is not enough to fully balance the rotating system as there will still be a moment created by the tilt in the principal axis of inertia. To reduce this tilt is it necessary to modify/shift the imbalance at two “balancing” planes, according to a two-plane (or dynamic) balancing technique. When this is performed the proper shift of the center of mass will also be achieved. The two balancing planes may be arbitrarily selected/located and need not be the same as the planes in which bearings supporting the shaft are located.
Many techniques and instruments for balancing a rotor in a rotation system are known, including single-plane balancing, multi-plane balancing, soft bearing instruments, stiff bearing instruments, resonance frequency instruments, time domain data acquisition, frequency domain data acquisition, etc., as appreciated by persons skilled in the art. Common to all known techniques is the need to adjust one or more masses on the rotor to provide the required shift of the center of mass and principal axis of inertia to bring them as close as possible to the axis of rotation. To achieve these adjustments in conventional techniques, it is necessary to stop the rotor (thus ceasing operation of the associated system), perform the adjustment by adding, removing, or moving masses, spin the rotor back up to an angular speed (which often is a reduced speed in comparison to the rotor's normal operating speed), re-test the imbalance, and repeat the process one or more times as needed. For large and very fast rotating systems, the time required to stop the rotation and subsequently attain the required rotational speed can be significant, for example on the order of many minutes or even hours. In many cases due to the fact that the rotor is tested in a separate enclosure than its actual stator, the rotational speed will be significantly lower than the nominal operating speed. Clearly this down time is disadvantageous, and is exacerbated when the balancing process must be repeated in an iterative manner, potentially requiring multiple spin/stop cycles to achieve an acceptable level of correction/adjustment in the imbalance.
Therefore, there is a need for providing improved solutions to balancing rotating components.